Conventionally the grinding of a syringe needle point is done by traversing a plurality of tubes which are joined and aligned by a tape along the grinding surface of a grinder with the ground plane of the tubes matching the plane of the grinding surface of the grinder.
Grinding takes place in a plurality of steps with the longitudinal angle of the tube to the grinding plane and the angular alignment of the tube about its axis being varied, whereby a syringe needle point with a main bevel and a side bevel can be produced.
In such a formation of the syringe needle point, as stated above a plurality of tubes are simultaneously ground. Therefore, the tube holder must extend in a horizontal direction, the holding pressure on all tubes must be uniform, the tips of the tubes being ground must be only minimally deflected so that slack will not occur even after a long period of service, and the angular alignment of each tube about its axis must be changed smoothly, reliably and uniformly.
For the sake of producing a syringe needle of high quality by exact grinding, the angle of the tube to the grinding plane and the angular alignment of the tube about its axis must be precisely changed.
When the grinding surface of the grinder becomes worn due to repeated use of the machine, the space between the grinding surface of the grinder and the ground plane of the tube must be adjusted to compensate for wear so that such space can always be maintained constant.
To the best knowledge of the inventor, there is no grinder for grinding a syringe needle point which fully meets all of these requirements.
The conventional tube holder holds the tube with difficulty, and the position of the held tube is not always satisfactory, thus calling for fine adjustment by a skilled worker.
Also a high degree of manual skill is needed for smooth, reliable and uniform rotation of the tube to change the angular alignment of the tube about its axis to carry out side bevel grinding.
As for the wear of the grinding surface of the grinder, a syringe needle point which has been ground at an empirically presumed timing of the grinding surface is inspected. If it is determined that a shortage of grinding of the tube is developing or has developed, the degree of shortage is checked by a micrometer or a magnifying glass, and the grinding surface of the grinder is moved closer to the tube by a distance corresponding to the amount of wear, and a corrective grinding operation is performed.
The corrective grinding operation also calls for a high degree of manual skill, and even such high skill cannot cope with a fine degree of wear of the grinding surface. Thus, the result of grinding becomes poor with wide variations in the grinding volume depending on the amount of correction, and syringe needles with irregular dimensions are produced. In the case of mass production, it is difficult to obtain products of uniform quality.
For these reasons, in conventional syringe needle point grinding operations a skilled worker has to continuously monitor the condition of the tube held in the tube holder, the angular alignment of the tube about its axis, and the condition of wear of the grinding surface of the grinder. Accordingly, full automation of the grinding operation has been deemed impracticable.